1. Field of the Invention
The present invention relates generally to coil design and is more particularly directed to coils used in electronic coin testers for testing a coin for the purpose of accepting a valid coin or rejecting a counterfeit coin in a coin-operated vending machine, game, telephone or the like.
2. State of the Prior Art
There are many kinds of coin operated devices and many ways to attempt to cheat them. Slugs, foreign coins and the retrievable coin-on-a-string are just a few examples. Therefore, there exist many coin testing devices that attempt to discriminate between acceptable coins and those that are not acceptable.
The art is crowded with numerous electromechanical coin testing devices that perform to a greater or lesser degree of accuracy and sensitivity. Among these are U.S. Pat Nos. 3,599,771, 3,741,363 and 4,469,213 which employ a pair of magnetic fields, each field present in a coin slot. In one slot, a sample coin is placed and in the other, a coin to be tested is made to pass through, often by the operator of the machine. Electronic circuitry monitors the magnetic fields in each slot to determine if the tested coin matches the sample coin using attenuation characteristics of the magnetic fields due to the sample and test coins as criteria. The narrower the attenuation detection band can be, i.e., how similar the test coin and sample coin attenuation characteristics need be before the coins match, the more sensitive and accurate the device becomes.
The coils used to generate the magnetic fields in the more sensitive prior art devices have been spiral coils having the outside periphery approximately equal to the diameter of the test and sample coins. Sometimes there have been, in one set, two or more coils in coaxial relation and sometimes they have been separated by circuit boards. The coils described generate flux patterns generally doughnut shaped with lines of magnetic flux cutting across the sample or test coin at the center and periphery of the coin. The coin's attenuation characteristics will, therefore, vary according to the coin's longitudinal attitude or physical position in relation to the coil. If the coin is even slightly off center, approximately half of the magnetic field will be left unaffected. This, in turn, creates inaccuracies in the device. Additionally, a separate set of test and sample coin slots must be used for each type of coin (i.e. nickel, dime, quarter, etc.) each having the outer periphery of the spiral coil to fit the size of the coin that the device is designed to detect. The following invention does not have these limitations.